Background of the Invention
The present disclosure relates generally to the field of submerged combustion melters and methods of use thereof to produce molten glass, and more specifically to methods and systems for making well-fined molten glass, and glass products therefrom, using one or more submerged combustion melters.
Background Art
A submerged combustion melter (SCM) may be employed to melt glass batch and/or waste glass materials to produce molten glass by passing oxygen, oxygen-enriched mixtures, or air along with a liquid, gaseous and/or particulate fuel (some of which may be in the glass-forming materials), directly into a molten pool of glass, usually through burners submerged in a glass melt pool. The introduction of high flow rates of products of combustion of the oxidant and fuel into the molten glass, and the expansion of the gases cause rapid melting of the glass batch and much turbulence and foaming.
Molten glass produced from an SCM is generally a homogeneous mixture of molten glass and fine bubbles. The bubbles may occupy up to 40 percent or more of the volume of molten glass produced with fine bubbles distributed throughout the molten mass of glass. For glass forming operations requiring well-fined (essentially void free) molten glass, a very large number of bubbles must be removed from the molten glass. The typical procedure for removing the bubbles is to allow a long enough residence time in one or more apparatus downstream of the SCM for the bubbles to rise to the surface and burst. Clearing bubbles from the molten glass is referred to as “fining” within the glass industry. Experience with SCMs has shown that the fining process can be very slow due to the bubbles collecting at the molten glass surface forming a layer of stable foam thereon. Formation of this foam layer in downstream fining chambers retards the fining mechanism as well as the heat penetration into the glass from fining chamber heating systems, such as combustion burners firing above the glass and/or electrical joule heating below the glass.
Use of skimmers within the foam layer has been used to hold back some of the upper foam layers allowing the lower, less foamy layers to pass through to later sections of channels downstream of the SCM. These efforts have been somewhat effective but may require multiple skimmers to obtain a foam free glass layer and surface. In addition, the skimmers are prone to failure during operation making them no longer useful in holding back the upper foam layers and can fall into and partially block the channel impeding some or all of the glass flow to downstream apparatus such as forming stations. It is also conventional to use a submerged throat positioned between a melter and a downstream channel, or between first and second sections of a melter; however, these throats are used primarily to serve as a demarcation between an upstream melting region and a downstream fining region. In effect, there is no attempt to separate any bubbles from the molten mass using conventional throats.
At least for these reasons, it would be an advance in the glass manufacturing art using submerged combustion melters if the foamy upper glass layer or layers, and the glass foam layer floating thereon, could be removed or separated from the fined glass without using multiple skimmers, thereby allowing formation of well-fined molten glass, and glass products using the well-fined molten glass.